Gaseous fluid nozzles have been used in the coating industry for at least two basic functions, the first of which may be classified as "doctoring means". In this use, the jet of gaseous fluid issuing from the nozzle impinges on a substrate, which has immediately before been coated in excess, to reduce and smooth the coating to the required standards as the substrate passes the nozzle.
Another basic use of gaseous fluid nozzles is in the strip processing industry as a "backing means", in which case, the jet is applied to one side of the moving strip, such as paper or plastic film, to maintain a uniform pressure against an object on the opposite side, such as a cooling roll or a rigid coating knife. One example of the "backing means" use is illustrated in the U.S. Pat. No. 3,113,884.
It is not intended to limit the principles of the present invention to the paper coating industry or the coating of substrates of this general type, but rather it is fully contemplated that the principles of the present invention may be applied to nozzles for many uses, some of which may not be presently known.
In most uses, it is important that the nozzle opening be uniform within close limits throughout the entire transverse length of the nozzle opening to insure a uniform coating on the moving substrate throughout its width. This can be a problem in many fluid nozzles due to the lack of stiffness in the transverse length of the lips forming the nozzle opening, or in the supporting nozzle body to which the lips are attached. Variations in the nozzle opening cause variations in the force output of the jet which produce variations in the coating thickness left on the strip.
In certain cases, it is desirable to be able to "contour" the nozzle opening, and in these cases, conformity to the desired shape is equally important. It is also extremely important in the coating industry that downtime and scrap be kept to a minimum. Since the coating station is usually only one part of a complicated and expensive system which provides a high rate of production, such as a paper board machine, or a steel galvanizing line, faults such as dirt in the nozzle produce scrap rapidly while stops disrupt many processes, and restarting after a stop may take many minutes, and produce much off standard product due to such disruption. A speck of dirt on or in the nozzle opening can cause a streak in a 200 inch wide strip running 1000 feet per minute or more. Since the nozzle usually has a convergent throat, particles which are too large to pass through the final orifice often lodge in the throat. The opening feature makes it easy to rid the nozzle of such blockages, saving lost time and lost production.
With the improved nozzle of this invention, dirt and streak problems can be corrected in seconds if dirt is loose, or a slightly longer period if the dirt is sticky and scrubbing is required. When the nozzle is restored to service, all settings and adjustments remain unchaged from the previous condition.
Many problems of existing nozzles have been eliminated by the improved nozzles of U.S. Pat. Nos. 3,314,163 and 4,513,915. However, use of the opening feature of these nozzle designs has been limited by the relatively high costs of their construction when compared with nonopening style nozzles, and also by the fact that constructing the nozzle in two sections requires that each section be large and stiff enough to provide a stable support for the nozzle lip attached thereto, so the resulting size alone makes it impossible to fit this type of nozzle into many coaters. In these "two support structure" nozzles, each half deflects outward between loading and control points, so the change in nozzle opening due to deflection between closure loading and control points is equal to the sum of the deflections of both halves. For these reasons, the advantages of the opening style have frequently been sacrificed, and non-opening nozzles containing the internal air distribution arrangement of U.S. Pat. No. 3,314,163, have frequently been furnished as a substitute by the assignee of these patents. In these non-opening style nozzles, the structures of the nozzles include a transversely extending tubular body with transversely extending lip mounting plates welded thereto, and transversely extending perforated metal walls welded between said plates, all of which provide a box-like structure giving stiffening reinforcement to the entire structure. This gives the nozzle a rigid, stable, relatively nondeformable structure.
Lip seats are carefully machined on the lip mounting plates, and thin rather flexible carefully ground lips which form the nozzle orifice or fluid discharge opening are solidly bolted thereto, using closely spaced bolts in slotted holes formed in the lips. The lips are flexible enough to allow deformation during placement for accurate alignment of the lips, and for adjustment of the nozzle opening between them. The setting of such lips in these non-opening nozzles and the corresponding opening therebetween, can be performed by a skilled mechanic using special tools, in twenty to sixty minutes. Lips when so set by bolting to the rigid structure, are sufficiently stable so that any necessity for readjustment is extremely rare unless a damaged lip must be replaced,or the size of the discharge opening must be changed.
An alternative, older, non-opening style nozzle construction consists of a U-shaped nozzle body of sufficiently heavy cross section to avoid appreciable deformation due to internal pressure, with the lip seats formed in the "U" extensions. Such nozzles have given satisfactory service, particularly in small transverse lengths, where the end plates tieing the two ends of the "U" shape together are close enough to effect stiffness of the complete structure.
One other known type of fluid nozzle construction having a pivotally mounted discharge opening forming lip is shown in U.S. Pat. No. 4,359,964. The fluid nozzle construction of this patent provides an adjustable nozzle opening by pivotally mounting the nozzle lip on an adjustable toggle linkage which moves the lip toward and away from a second fixed lip to provide access into the nozzle interior for cleaning. One disadvantage of a nozzle following the teachings of this patent lies in the fact that the lip is free to rotate about the groove in the nozzle body which is its only rigid point of support, and this arcuate motion in limited only by a relatively unstable adjustable toggle linkage which has passed over center. The distance the toggle pin can pass center would also be limited by the lips coming together when the toggle passes center. Therefore, if the user of a nozzle similar to that shown in this patent tries to set an orifice of, for example, 0.030", and the design has the proportions as shown in the structure of the patent, the distance of the pivot below center would be limited to approximately 0.030", hardly enough for stability.
Also, the stop mechanism of prior nozzles as shown in U.S. Pat. No. 4,359,964 would have to be arranged to stop the downward motion of the pivot before it travels 0.030" below the straight line through centers. Without such a stop, the device would allow the lip to continue to open under the influence of the interal fluid pressure in the nozzle, and the construction would no longer limit the orifice height. A further disadvantage of such a nozzle is that the pivoted lip throughout its length and width from the pivot location to the orifice is subject to the entire pressure of the internal fluid within the nozzle. This makes it extremely difficult to control the amount of deflection along the transverse length of the lip, thereby vastly increasing the difficulty of maintaining the desired discharge opening uniformly throughout the nozzle transverse length.
Therefore, the need has existed for a fluid nozzle in which one of the nozzle discharge opening lips can be lifted away from the other to open the nozzle for cleaning, but when in operating position is clamped tightly against and is stiffened by the entire nozzle structure; in which the movable lip can be returned upon reclosing to the exact previous setting of the discharge opening; and in which air pressure within the nozzle acts only on a limited area of each lip, thus minimizing the bending of the lip along an axis parallel to its transverse length; since such bending increases the height of the discharge opening. There is also, but not always, a need for such a nozzle in which the height of the discharge opening at all points across its transverse length can be adjusted while in operating position by a single adjustment, or can be shaped by segmental adjustments.